Question

A camera objective has an aperture diameter $d$. If the aperture is reduced to diameter $d/2$, the exposure time under identical conditions of light should be made

• A. $\sqrt{2}$ fold
• B. $2$ fold
• C. $2\sqrt{2}$ fold
• D. $4$ fold

Answer 1

Answer: (D)

$4$ fold

Time of exposure $\propto \frac{1}{(Aperture{)}^2}$

hence if apperuture is halfed then exposure is four times.